This invention relates to the sensing of the presence of a flame produced by a burner within a furnace and in particular to the optical sensing of such a burner flame.
Photo optical sensors have heretofore been used to sense the presence of a flame produced by a burner of a furnace. These photo optical sensors are positioned relative to the burner so as to respond to the light emitted by the flame produced by the burner. It is to be appreciated that such sensing normally occurs under a variety of background lighting conditions. These background conditions may introduce a significant level of noise into any electrical signal generated by the photo sensor. This background noise must be dealt with by the circuitry associated with the photo sensor so as to produce a signal that can be relied upon to indicate the presence of a flame.